To very efficiently supply an object rotating at high speed or a small object such that an electric wire cannot be connected thereto with power from the external by radio, by causing matching of a power supply frequency at which power is supplied with the tuning frequency of a transmission circuit at all times.

The phase difference between the resonance frequency of a primary coil 100 and a power supply frequency at which power is supplied is detected through the phase detection circuit in a tuning unit 300. The frequency of power supply fed to the primary coil 100 is controlled using VCO 4 in a power supply unit 400 according to the phase-detected signal, in order to have the resonance of the primary coil 100 trued with the frequency of a power supply fed to the primary coil 100. That is, automatic tracking closed-loop control is exercised to follow the tuning frequency of the primary coil 100. As a result, a power supply frequency which matches the tuning frequency can be kept supplied at all times, even if tuning out occurs. Therefore, power can be supplied with stability and high transmission efficiency.